Techniques for Reducing the Connected-Standby Energy Consumption of Mobile Devices

Modern mobile devices, such as smartphones, tablets, and laptops, are idle most of the time but they remain connected to communication channels even when idle. This operation mode is called connected-standby. To increase battery life in the connected-standby mode, a mobile device enters the deepest-runtime-idle-power state (DRIPS), which minimizes power consumption and retains fast wake-up capability. In this work, we identify three sources of energy inefficiency in modern DRIPS designs and introduce three techniques to reduce the power consumption of mobile devices in connected-standby. To our knowledge, this is the first work to explicitly focus on and improve the connected-standby power management of high-performance mobile devices, with evaluations on a real system. We propose the optimized-deepest-runtime-idle-power state (ODRIPS), a mechanism that dynamically: 1) offloads the monitoring of wake-up events to low-power off-chip circuitry, which enables turning off all of the processor's clock sources, 2) offloads all of the processor's input/output functionality off-chip and power-gates the corresponding on-chip input/output functions, and 3) transfers the processor's context to a secure memory region inside DRAM, which eliminates the need to store the context using on-chip high-leakage SRAMs, thereby reducing leakage power. We implement ODRIPS in Intel's Skylake client processor and its associated Sunrise-Point chipset. An analysis of ODRIPS on a real system reveals that it reduces the platform average power consumption in connected-standby mode by 22%. We also identify an opportunity to further reduce ODRIPS power by using emerging low-power non-volatile memory (instead of DRAM) to store the processor context.